Soft Template-Induced Porous Polyvinylidene Fluoride Membrane for Vanadium Flow Batteries

Vanadium flow batteries(VFBs)are considered ideal for grid-sc ale,long-duration energy storage applications owing to their decoupled output power and storage capacity,high safety,efficiency,and long cycle life.However,the widespread adoption of VFB s is hindered by the use of expensive Nafion membranes.Herein,we report a soft template-induced method to develop a porous polyvinylidene fluoride(PVDF)membrane for VFB applications.By incorporating water-soluble and flexible polyethylene glycol(PEG 400)as a soft template,we induced the aggregation of hydrophilic sulfonated poly(ether ether ketone),resulting in phase separation from the hydrophobic PVDF polymer during membrane formation.This process led to the creation of a porous PVDF membrane with controllable morphologies determined by the polyethylene glycol content in the cast solution.The optimized porous PVDF membrane enabled a stable VFB performance for 200 cycles at a current density of 80 mA/cm^(2),and the VFB exhibited a Coulombic efficiency of 95.2%and a voltage efficiency of 87.8%.These findings provide valuable insights for the development of highly stable membranes for VFB applications.

Dye-sensitized Solar Cells with Higher J_(sc) by Using Polyvinylidene Fluoride Membrane Counter Electrodes

A flexible counter electrode(CE) for dye-sensitized solar cells(DSCs) has been fabricated using a micro-porous polyvinylidene fluoride membrane as support media and sputtered Pt as the catalytic material.Non-conventional structure DSCs have been developed by the fabricated CEs. The Pt metal was sputtered onto one surface of the membrane as the catalytic material. DSCs were assembled by attaching the Ti O2 electrode to the membrane surface without Pt coating. The membrane was with cylindrical pore geometry. It served not only as a substrate for the CE but also as a spacer for the DSC. The fabricated DSC with the flexible membrane CE showed higher photocurrent density than the conventional sandwich devices based on chemically deposited Pt/FTO glass, achieving a photovoltaic conversion efficiency of 4.43%. The results provides useful information in investigation and development of stable, low-cost, simple-design, flexible and lightweight DSCs.

Effect of Packaging Material on Piezoelectric Response of Sensor with Electrospinning Polyvinylidene Fluoride (PVDF) Nanofiber Web

The polyvinylidene fluoride(PVDF)nanofiber web by electrospinning technology has the characteristics of fast response,high sensitivity,wide range of pressure,etc.,and provides new sensitive materials for the sensor testing the dynamic pressure such as foot pressure during walking.Because of the nanofiber mesh structure,it must be packaged to collect piezoelectric charge and bear strong mechanical behavior before industrial practice.The PVDF nanofiber web is usually packaged by incorporating a pair of flexible electrode as well as the lead of signal output.This present work will introduce the detailed packaging process and technology of PVDF nanofiber web,and three different types of packaging electrode materials(adhesive copper foil tape,indium tin oxide(ITO)thin plate,and adhesive conductive cloth)in previously published literatures are compared by the piezoelectric response of their sensor prototypes to a periodic mechanical activation.The results showed that the surface property of packaging material had a significant effect on the piezoelectric response of sensor by PVDF nanofiber web.For PVDF nanofiber web sensor,therefore,it needed a deep investigation on the specific packaging technology in terms of different working conditions.

Preparation and Characterization of the Modified Polyvinylidene Fluoride (PVDF) Hollow Fibre Microfiltration Membrane

A novel thermally induced graft polymerization technique was used to modify a polyvinylidene fluoride （PVDF） hollow fibre microfiltration membrane. An artificial neural network （ANN） was applied to optimize the prepared condition of the membrane. The optimized dosing of acrylic acid （AA）, acrylamide （AM）, N, N＇- methylenebisacrylamide （NMBA） and potassium persulphate （KSP） designed by ANN was that AA was 40.63 ml/L; AM acted as 6.25 g/L; NMBA was 1.72 g/L and KSP was 1.5 g/L, respectively. The thermal stability of the PVDF modified hollow fibre membrane （PVDF-PAA） was investigated by thermogravimetric （TG） and differential scanning calorimetry （DSC） analysis. The polycrystallinity of the PVDF-PAA membrane was evaluated by X-ray diffraction （XRD） analysis. The complex formation of the modified membrane was ascertained by Fourier transform infrared spectroscopy （FTIR）. The morphology of the PVDF-PAA membrane was studied by environmental scanning electron microscopy （ESEM）. The surface compositions of the membrane were analyzed by X-ray photoelectron spectroscopy （XPS）. The adsorption capacity of Cu^2＋ ion on the PVDF-PAA hollow fibre membrane was also investigated.

Effect of Polyvinylidene Fluoride Hollow Fiber Membranes on Mass Transfer of Samarium

The influence of swelling and stripping acidity on the mass transfer coefficient based on water phase and the inner diameters of membranes were studied with P507-HCl-Sm as working system in the two different kinds of hollow fiber membranes. Effects of extractant concentration, H+ concentration in aqueous phase and Sm3+ concentration on extraction rate were discussed and the corresponding reaction series were obtained. According to the investigations on the interfacial kinetics, the reaction kinetics equation and reaction rate constant were obtained.

PREPARATION AND CHARACTERIZATION OF ION EXCHANGE MEMBRANES BASED ON POLYVINYLIDENE FLUORIDE

A new ion exchange membrane based on polyvinylidene fluoride (PVDF) and sulfonated poly(styrene-divinylbenzene) was prepared by in-situ polymerization. The incorporation of sulfonic groups into the polyvinylidene fluoride composite membrane was confirmed by infrared spectroscopy (IR), ion exchange capacity (IEC) and energy dispersive X-ray analysis (EDAX). Area resistance, IEC and water uptake of the treated membrane were evaluated. When 20% of the crosslinked membrane was sulfonated at 80degreesC for 22 h, the PVDF ion exchange membrane can attain 0.8 Omega . cm(2) area resistance in NaCl aqueous solution at 25degreesC, IEC is as high as 2.43 millimoles per grain of the wet membrane. The hydrophilicity of PVDF membrane is also significantly improved after treatment. When 60% of crosslinked membrane was sulfonated at 80degreesC for 6 h, water uptake of the treated membrane can attain 64.7%.

Morphology of Polyvinylidene Fluoride Based Gel Polymer Electrolytes

Two series of polyvinylidene fluoride (PVDF) based gel polymer electrolytes, with different LiClO 4 or propylene carbonate (PC) content, were prepared and analyzed by infrared spectrometer, differential scanning calorimetry, scanning electron microscope and complex impedance spectrometer. The results show that there are great interactions between PVDF, PC and lithium cations. Both LiClO 4 and PC content lead to evident change of the morphology of the gel polymer electrolytes. The content of LiClO 4 and PC also influences the ionic conductivity of the samples, and an ionic conductivity of above 10 -3 S·cm -1 can be reached at room temperature.

Contact Angle Prediction Model for Underwater Oleophobic Surfaces Based on Multifractal Theory

Traditional microstructure scale parameters have difficulty describing the structure and distribution of a roughmaterial’s surface morphology comprehensively and quantitatively. This study constructs hydrophilic and underwateroleophobic surfaces based on polyvinylidene fluoride (PVDF) using a chemical modification method, and the fractaldimension and multifractal spectrum are used to quantitatively characterize the microscopic morphology. A new contactangle prediction model for underwater oleophobic surfaces is established. The results show that the fractal dimension ofthe PVDF surface first increases and then decreases with the reaction time. The uniformity characterized by the multifractalspectrum was generally consistent with scanning electron microscope observations. The contact angle of water droplets onthe PVDF surface is negatively correlated with the fractal dimension, and oil droplets in water are positively correlated.When the fractal dimension is 2.0975, the new contact angle prediction model has higher prediction accuracy. Themaximum and minimum relative deviations of the contact angle between the theoretical and measured data are 18.20%and 0.72%, respectively. For water ring transportation, the larger the fractal dimension and spectral width of the materialsurface, the smaller the absolute value of the spectral difference, the stronger the hydrophilic and oleophobic properties, andthe better the water ring transportation stability.

Improvement of hydrophilicity of porous PVDF membranes with LiCl additives

Porous polyvinylidene fluoride（PVDF）membranes blended with LiCl are prepared through the phase inversion method to obtain a good support layer for air dehumidification.The hydrophilicity of the resulting membrane is evaluated by water contact angle measurements and vapor adsorption tests.The moisture permeation performance of the membrane is measured by permeation tests in terms of total mass transfer coefficients and moisture permeability rates.It is found that water contact angles and water vapor adsorption capacities increase with the increasing LiCl content in the casting solution.As the LiCl content increases,the total mass transfer coefficient increases slightly at a low LiCl content（below 2.5%）and then improves greatly at a high LiCl content（above 2.5%）,whereas the moisture permeation rate increases.The results demonstrate that LiCl can remarkably improve the hydrophilicity of PVDF membranes,and then greatly enhance moisture permeation performance.

Construction of Renewable Superhydrophobic Surfaces via Thermally Induced Phase Separation and Mechanical Peeling

We report a simple preparation method of a renewable superhydrophobic surface by thermally induced phase separation （TIPS） and mechanical peeling. Porous polyvinylidene fluoride （PVDF） membranes with hierarchical structures were prepared by a TIPS process under different cooling conditions, which were confirmed by scanning electron microscopy and mercury intrusion porosimetry. After peeling off the top layer, rough structures with hundreds of nanometers to several microns were obtained. A digital microscopy determines that the surface roughness of peeled PVDF membranes is much higher than that of the original PVDF membrane, which is important to obtain the superhydrophobicity. Water contact angle and sliding angle measurements demonstrate that the peeled membrane surfaces display super- hydrophobicity with a high contact angle （152°） and a low sliding angle （7.2°）. Moreover, the superhydrophobicity can be easily recovered for many times by a simple mechanical peeling, identical to the original superhydrophobicity. This simple preparation method is low cost, and suitable for large-scale industrialization, which may offer more opportunities for practical applications.

聚偏氟乙烯改性氧化石墨烯智能柔性膜的湿电性能研究

石墨烯在湿气产电、水蒸发诱导产电、湿气响应驱动器等领域显示出强大的应用潜力,强化石墨烯基材料的湿电性能具有重要的现实意义。将一定量的聚偏氟乙烯(polyvinylidene fluoried,PVDF)引入到氧化石墨烯(graphene oxide,GO)薄膜中,在维生素C存在时,促使成膜过程中GO发生部分还原,最终形成一种均匀分散的PVDF复合膜。红外谱图显示,复合膜具有GO和PVDF的双重特征;扫描电子显微镜扫描结果表明,PVDF在GO内部呈现树叶状分布,提高了膜的稳定性;X射线衍射采集数据表明了GO存在部分还原现象;湿气响应实验表明,得到的复合材料的端电压和端电阻随湿度变化呈现规律性变化,具有很好的响应性能,为智能材料的研发奠定了基础。

A Self-Powered Breath Analyzer Based on PANI/PVDF Piezo-Gas-Sensing Arrays for Potential Diagnostics Application

The increasing morbidity of internal diseases poses serious threats to human health and quality of life.Exhaled breath analysis is a noninvasive and convenient diagnostic method to improve the cure rate of patients. In this study, a self-powered breath analyzer based on polyaniline/polyvinylidene fluoride(PANI/PVDF) piezogas-sensing arrays has been developed for potential detection of several internal diseases. The device works by converting exhaled breath energy into piezoelectric gassensing signals without any external power sources. The five sensing units in the device have different sensitivities to various gas markers with concentrations ranging from 0 to 600 ppm. The working principle can be attributed to the coupling of the in-pipe gas-flow-induced piezoelectric effect of PVDF and gas-sensing properties of PANI electrodes. In addition, the device demonstrates its use as an ethanol analyzer to roughly mimic fatty liver diagnosis.This new approach can be applied to fabricating new exhaled breath analyzers and promoting the development of self-powered systems.

PTC/NTC Behavior of PVDF Composites Filled with GF and CF

Conductive polyvinylidene fluoride（PVDF）matrix composites filled with graphited fiber（GF）or carbon fiber（CF）were prepared by the melt-mixing method.The breakage and length distribution of the fibers in the polymer matrix were studied by scanning electron microscope（SEM）and optical microscope（OM）observations,respectively. The differences in the positive temperature coefficient（PTC）effects of the composites were mainly attributed to inter-fiber contact ability.The elimination of the negative temperature coefficient（NTC）effect for CF/PVDF composite was because of an increase in the viscosity of the polymer matrix.With the same filler content,CF could be more effective,to eliminate the NTC effect when compared with GF.Addition of 2%CF（mass fraction）in the PVDF composite with 7%GF（mass fraction）could effectively eliminate the NTC phenomenon of the composite.

Wind Energy Harvesting Using Flexible Piezoelectric Device

A FPED （flexible piezoelectric device） composed of PVDF （polyvinylidene fluoride） and functional resin has been developed to generate electric power from wind energy with wide range in frequency. It was cleared that electrical characteristics of the FPED generated by wind power and availability of an attached bluff body in uniform wind. Moreover, electric performance of the FPED which is laminated with a stretching resin and has a roughness surface such as woolen and small hemisphere, was validated. It was shown that both a force caused by breeze and wind energy with wide range of spectrum could be harvested effectively using the FPED.

STUDIES ON THE CHAIN STRUCTURAL EFFECT OF PVDF AND VDF (52)/TrFE(48) COPOLYMER BY MEANS OF THE METHOD OF DIELECTRIC RELAXATION

Through improvements on a fully commercial and automatic system measuring frequency andtemperature spectra of the complex elastic, dielectric, and piezoelectric constants of polymerfilms, the precision for measuring complex dielectric constants achieved 2‰ from original 1%.The complex dielectric constants of PVDF, VDF （95 ）/VF （5）, VDF （52）/TrFE （48） and VDF（47. 5）/TrFE（47. 5）/HeFP （5） over a range of-120-140℃, 10-2-10;Hz were measured bythe described system. The diminution of chain regularity due to 5mol% vinyl fluoride in the chainof PVDF led to disappearing of α-relaxation and increase in T;（3℃） of VDF （95）/VF （5）.Because of the spatial impediment of 5mol% HeFP in copolymer chain, the Curie point of VDF（52）/TrFE（48） decreased by 30℃ and T;by 3℃. The behavior of dielectric relaxation indicatedthat 5mol% vinyl fluoride and HeFP made the relaxation strength of noncrystalline regionreduced, the activation energy of local relaxation increased and the relaxation time prolonged respectively.

Damage Identification in Beam-Type Structures Using Pseudo Strain Energy Density and Grey Relation Coefficient

Based on pseudo strain energy density (PSED) and grey relation coefficient (GRC), an index is proposed to locate the damage of beam-type structures in time-domain. The genetic algorithm (GA) is utilized to identify the structural damage severity of confirmed damaged locations. Furthermore, a systematic damage identification program based on GA is developed on MATLAB platform. ANSYS is employed to conduct the finite element analysis of complicated civil engineering structures, which is embedded with interface technique. The two-step damage identification is verified by a finite element model of Xinxingtang Highway Bridge and a laboratory beam model based on polyvinylidens fluoride (PVDF). The bridge model was constructed with 57 girder segments, and simulated with 58 measurement points. The damaged segments were located accurately by GRC index regardless of damage extents and noise levels. With stiffness reduction factors of detected segments as variables, the GA program evolved for 150 generations in 6 h and identified the damage extent with the maximum errors of 1% and 3% corresponding to the noise to signal ratios of 0 and 5%, respectively. In contrast, the common GA-based method without using GRC index evolved for 600 generations in 24 h, but failed to obtain satisfactory results. In the laboratory test, PVDF patches were used as dynamic strain sensors, and the damage locations were identified due to the fact that GRC indexes of points near damaged elements were smaller than 0.6 while those of others were larger than 0.6. The GA-based damage quantification was also consistent with the value of crack depth in the beam model.

Preparation of Air Film for Medical Infusion Device and Study on Air Permeability and Water Resistance

Polypropylene melt-blown nonwoven was used as the substrate for the preparation of an air film. The nonwoven was immersed in the casting solution at first,and then respectively placed in the first coagulation bath,the second coagulation bath and the finishing liquid containing fluorine additive aqueous solution of 20 g/L. At last,the high temperature drying was carried out to obtain the air permeable and water resistant air film. With analyses and comparisons of the isopropanol alcohol content,the residence time of air,the composition of the first coagulation bath and the residence time of the first coagulation,the optimum parameters were found and the air film had an air permeability of 4. 7 L/min,a water blocking pressure of 16 kPa,a contact angle of 134. 2°,and a mean pore size of 2. 089 1 μm.

Preparation and Characterization of Multi Shape ZnO/PVDF Composite Materials

Two different morphologies of ZnO（lotus-shaped, rod-shaped） and ZnO/PVDF composite materials were prepared. The morphologies of ZnO and composite materials were characterized by scanning electron microscopy（SEM） and transmission electron microscopy（TEM）. Fourier transform infrared spectroscopy（FT-IR）, thermal gravimetry（TG）, and X-ray diffraction（XRD） were also used to characterize the chemical structures and phase composites of ZnO and ZnO/PVDF composite materials. Breakdown voltage, dielectric constant and dielectric loss of ZnO/PVDF composite materials were also tested. Microstructure analysis showed that ZnO nanoparticles dispersed uniformly in the matrix. And the dielectric constant expresses a significantly improvement while the dielectric loss and breakdown voltage expresses no significant change. Moreover, dielectric constant keeps an improvement tendency with increasing content of ZnO.

Using polyvinylidene fluoride to improve ignition and combustion of micron-sized boron powder by fluorination reaction

Boron has a promising application in the field of propellants due to its high calorific value.However,the difficulty of ignition and the poor combustion efficiency of boron(B)have severely limited its efficient application.In response to this issue,this paper proposes to improve the ignition and combustion performance of micron-sized boron by the Polyvinylidene Fluoride(PVDF)coating.The effect of PVDF content on the B combustion performance was systematically studied using a Thermogravimetry-Differential Scanning Calorimetry(TG-DSC),a Transmission Electron Microscope(TEM),an X-Ray Diffractometer(XRD),a laser Particle Size Analyzer(PSA),and a high-speed camera.The results show that PVDF can significantly reduce the initial oxidation temperature of B powder and increase its reaction heat.When the PVDF content is 23wt%,the reaction heat and the combustion intensity of B powder reach the maximum and are significantly higher than those of the uncoated B powder.Moreover,the fluorination reaction that occurs during the combustion process not only can effectively shorten the combustion time of B powder,but also has a positive effect on its flame intensity and propagation speed,and it significantly reduces B particle agglomeration,which improves the combustion efficiency significantly.This study lays the foundation for the application of PVDF modified B in B-based solid propellants.

High-efficiency preparation of multifunctional conjugated electrospun graphene doped PVDF/CF yarns for energy harvesting and human movement monitoring in TENG textile

Portable power is an effective solution to realize self-powered sensors for wearable devices,promoting future sustainable development.Membrane-based triboelectric nanogenerators(M-TENGs)have emerged as a promising technology for harvesting biomechanical energy from human motion owing to their advantages,such as simple structure,lightweight design,and efficient energy conversion.However,the poor durability,low adaptability,and un-washability of two-dimensional membrane materials have largely hindered their application in wearable electronics.In this study,we propose a sheath-core polyvinylidene fluoride(PVDF)/graphene(G)-carbon fiber(CF)yarn fabricated via conjugate electrospinning,comprising a commercial CF core and an electrospun graphene-doped PVDF sheath,which improves the fatigue resistance of electrospun nanofiber films under prolonged friction and keeps a high degree of freedom.The resulting electronic textile,woven with the large-scale electrospun PVDF/G-CF yarn,demonstrates a remarkable power density of 25.5 mW·m^(-2).The tight distribution of PVDF/G nanofibers on the textile surface ensures excellent softness,washability,and durability.Furthermore,the electrospun PVDF/G-CF textile exhibits significant potential in pressure sensing,self-powered operation,and motion detection,making it highly suitable for wearable electronics applications.